1. Field of the Invention
This invention relates generally to an apparatus for rotationally casting a portion of a tire, and, more specifically, to an apparatus that has a cap and ail outer ring that are separately and rotatably attached to a molding apparatus with a pouring slot between them for centrifugally molding the spokes of a non-pneumatic tire from polyurethane or some other suitable material.
2. Description of the Related Art
An emerging field in tire development involves the manufacture and use of non-pneumatic or hybrid tires that do not depend solely on gas to support the tire structurally as these dyes are not prone to deflation, which can render standard pneumatic, tires inoperable. An example of such a tire is disclosed by U.S. Pat. No. 7,201,194, which is commonly owned by the applicant of the present application. The content of this patent is incorporated herein by reference for all purposes in its entirety. In an exemplary embodiment of the '194 patent, the non-pneumatic tire includes an outer annular shear band and a plurality of web spokes that extend transversely across and radially inward from the annular shear band and are anchored in a wheel or hub. In certain embodiments, the annular shear band may further comprise a shear layer, at least a first membrane adhered to the radially inward extent of the shear layer and at least a second membrane adhered to the radially outward extent of the shear layer. In addition to the ability to operate without a required inflation pressure, the invention of U.S. Pat. No. 7,201,194 also provides advantages that include a more uniform ground contact pressure throughout the length of the contact area. Hence, this tire mimics the performance of a pneumatic tire.
FIG. 1 shows such a tire that defines a radial direction R. For reference, all the reference numerals in the 100's used herein refer to the tire features and previous mold design while all reference numerals in the 200's used herein refer to a new and improved molding apparatus according to an embodiment of the present invention. The tire 100 comprises a tread 102 that is attached to the outward extent 104 of the spokes 106, which in turn, are connected to a hub or wheel 108 at their inward extent 110 by means known in the art such as by molding spokes between the hub 108 and the tread 102, which have been prepared for suitable bonding to the polyurethane. For the version of the tire 100 shown, the spokes 106 are formed by pouring as polyurethane liquid into a rotational mold where the liquid is spread via centrifugation and then cured or hardened, it can also be seen that the spokes 106 are grouped in pairs and that the individual spokes 106, 106″ within each pair are consistently spaced from each other and that each pair is spaced consistently from the adjacent pair around the circumference of the tire. The spacing within each pair and the spacing between each adjacent pair do not need to be the same. As described by the Abstract and col. 2, lines 28-41 of the '194 patent, the spokes 106 support the tire 100 in tension near the top of the tire 100 and not in compression. Instead, the spokes 106 at the bottom of the tire near the contact patch, which is where the tread 102 of the tire 100 contacts the road, compress or buckle easily. This helps the tire to simulate the pneumatic support function of a pneumatic tire.
Looking now at FIG. 2, a top view of as mold 112 according to a previous design is shown with the top portion 116 of the mold 112 in a translucent state so that the cavities 114 that form the spokes 106 of the tire 100 can be seen. It also defines a radial direction R that is the same as the radial direction as the tire whose spokes it manufactures, FIG. 2A, is a sectional view of the mold 112 taken along lines 2A-2A of FIG. 2. The mold 112 includes a bottom portion 118 that can be clamped onto a platen of a rotational molding turntable (not shown) by means commonly known in the art. The cavities 114 that form the spokes 106 are defined by interarticulating cores 120 that extend from the bottom and top portions 116, 118 of the mold 112 in an alternating pattern around the circumference of the mold 112. As best seen in FIG. 2A, two cores 120 located diametrically opposite of each other project down from the top portion 116 and shut off on slightly contoured surfaces 122 found on the bottom portion 118 of the mold 112 without projecting or telescoping into the bottom portion 118 of the mold 112. It is to be understood that similar cores extend from the bottom portion and shut off on slightly contoured surfaces found on the top portion of the mold due to the alternating arrangement of the cores. Taper pins 113 are also shown that are used for mold alignment when the mold halves are assembled. Sometimes, additional taper pins (not shown) are located on the ends of the cores that mate with pockets on the opposing mold half for fine tuning, the alignment of the cores.
Looking at both FIGS. 2 and 2A, the top portion 116 of the mold 112 includes a cap 124 that is centered with respect to the cylindrical shape of the mold 112 and an outer ring 126 that is concentric with the cap 124 when both components are attached to the bottom portion 118 of the mold 112. This arrangement creates a small gap or pouring slot 128 around the periphery of the cap 124 for introducing the polyurethane to form the spokes as will be discussed in more detail later. Both the outer ring 126 and the cap 124 can be attached and detached separately from the bottom portion 118 of the mold 112 using bolts 130, screws or other means commonly known in the art. Usually, the bolts 130 are found with their heads exposed from the exterior surface of the top portion 116 of the mold 112 to facilitate access for tightening and loosening the belts 130. Some common mold features such as vents for helping proper mold fill by allowing the escape of trapped gas are not discussed herein as they are not pertinent to the present invention. Also the cores are shown to be solid extensions of the mold halves 116, 118 but in actuality these are often separate inserts that are retained within the mold halves 116, 118 and that can be easily replaced should a core 120 be damaged.
The mold 112 can be used in the following manner to create the spokes 106 of the tire 100, as depicted by FIGS. 2A and 2B. First, the outer ring 126 and cap 124 of the top portion 116 of the mold 112 are removed so access to the inner annular pocket 132 of the bottom portion 118 of the mold 112, which is configured for receiving the hub or wheel 108 of the tire 100, and the outer annular slot 134 of the bottom portion 118 of the mold, which is configured for receiving the bottom half of the tread 102 of the tire 100, is possible. Then, the user places the hub 108 into the inner annular pocket 132 which has a ring shaped wall 136 that defines its radially innermost extent and that has chamfers 138 near its top and bottom for helping to properly locate the hub 108 so that it is concentric with the mold 112. In like fashion, the tread 102 is lowered into the outer annular slot 134 found in the bottom portion 118 of the mold and guided into a substantially concentric position with respect to the mold by alignment features (not shown).
Also as best seen in FIG. 211, once the hub 108 and tread 102 are properly positioned, the outer ring 126 is then placed into position so that its cores 120 are positioned between the cores of the bottom portion of the mold and so that its outer annular slot 140, which is substantially a mirror image of the outer annular slot 134 of the bottom portion 118 of the mold about its parting line 142, holds the remaining portion of the tread 102 that protrudes from the bottom portion 118 of the mold. Next, the cap 124 is centered with respect to the hub 108, and therefore with the mold as well, via its chamfer 141 as it is placed onto the hub 108. The outer ring 126 and cap 124 are then secured to the bottom portion 118 of the mold 112 as previously described. Finally, the mold 112 is rotated and heated polyurethane is poured into the mold by a nozzle (not shown) that is positioned directly above the pouring slot 128. This is possible since the pouring slot 128 is unobstructed as the mold 112 rotates. This slot leads to the cavities 114 that define the spokes 106. Centrifugation causes the polyurethane to fill out all of the spokes and the heat supplied to the mold is transferred to the liquid, helping the polyurethane to harden and cure by keeping it warm. The spokes 106 now extend from the hub 108 to the tread 102, allowing the spokes to bond to the hub and tread during the curing process.
Once the spokes 106 have cured, it is time for the tire 100 to be removed from the mold 112. First, the outer ring 126 is unfastened from the bottom portion 118 of the mold 112 and lifted vertically so that its cores 120 can disengage or demold from the spokes 106 that have just been created and so that the outer annular slot 140 of the top portion of the mold can break free of the tread 102 of the tire. It is advantageous to leave the cap 124 secured to the bottom portion 118 of the mold during this step as this keeps the hub 108 trapped, which is now connected to the tread 102 by way of the spokes 106, which in turn helps to keep the tire 100 attached to the bottom portion 118 of the mold 112 when the outer ring 124 is being removed. This helps to ensure that the tire remains on the bottom portion of the mold. This is desirable as lifting the outer ring with the tire attached is difficult to do by hand and removing the tire from the top portion of the mold when they are both elevated could be problematic. Once the outer ring 126 has been successfully removed, the cap 124 can then also be removed and the tire 100 is then free to be pulled out of the bottom portion 118 of the mold 112.
Thus, this apparatus necessitates a manufacturing process that is done primarily by manual means. For example, an operator needs to manually attach and detach the outer ring and cap of the mold in order to make the spokes for each tire because the top portions of the mold are not attached to a top platen of a molding press. This is too time consuming and costly to provide non-pneumatic or hybrid tires with their enhanced reliability, i.e. less downtime due to tire deflation, to consumers in an efficient and cost effective manner.
Accordingly, it is desirable to find an apparatus that allows such tires to be manufactured using a mold that has first and second portions that are attached to the first and second platens of a molding press, which allows the mold to be closed and opened automatically without human intervention, it would be particularly useful if such an apparatus could be designed to allow a liquid to be introduced into a mold without obstructing the liquid's path for filling the mold as the mold rotates. Finally, providing means for keeping the tire on a predetermined portion of the mold where an ejection system and/or tire handling system are provided would be desirable.